Hans-Toni Ratte

Life-strategy shift by intraspecific interaction in Daphnia magna : change in reproduction from quantity to quality

Abstract In Daphnia magna, high animal density causes a mutual intraspecific influence, called life-strategy shift by intraspecific interaction (LiSSII). We investigated mothers (F0), living singly or in groups of four per 50 ml, and their F1 offspring. Clutch sizes of F0 daphnids living in groups were smaller than those of singly living ones. However, the F1 neonates were bigger in size, had higher dry weights and contained more lipids. They were also able to survive longer starvation periods. If these F1␣daphnids were again kept in groups of four, the effects of LiSSII on some life-history parameters were stronger. As compared to group-living F0 daphnids, juvenile development time was prolonged from 7.5 to 10.0 days. In contrast, body size was reduced and the further reduction in offspring number was slight. The F2␣neonates exhibited the same change towards bigger size and higher dry weight as observed in the F1. In contrast F1 daphnids, that were the offspring of daphnids living in groups but were kept singly were bigger and produced more offspring than single daphnids that were the offspring of daphnids kept singly. The neonates of the former were bigger in size and heavier. It is suggested that for the F0 generation the ecological significance of the LiSSII effects is an increase in both the parent and offspring survival probability when food is limited. LiSSII acts before food conditions deteriorate seriously. Daphnids affected by LiSSII invest less of their biomass into offspring. Offspring release is well-timed and quality is better, at the expense of quantity. Under favourable environmental conditions, F2 daphnids that are the offspring of mothers affected by LiSSII appeared well adapted to fast recolonisation when living at low density.

The combined effects of temperature and food consumption on body weight, egg production and developmental time in Chaoborus crystallinus De Geer (Diptera: Chaoboridae)

SummaryChaoborus crystallinus fourth-instar larvae were reared individually at 14°, 17° and 20° C under different food conditions. Daphnia magna of 1.25 mm average length served as prey. The following were measured: amount of prey ingested, larval weight gain, duration of fourth instar, body weight of the adults, and egg number per female. At a given temperature, the body weight, egg-number and developmental rate increased with food consumption. At a given food consumption, higher temperatures caused a decrease in body weight and egg number, and an increase in developmental rate. Gross production efficiencies for fourth-instar larvae were highest at temperatures around 17° C. The results clearly indicate that from an energetic point of view higher temperatures are disadvantageous. In C. crystallinus vertical migration is evidently a way of lowering the temperature to which the animals are exposed and hence optimizing food conversion into biomass and offspring production, especially if prey densities are below the saturation level.

Thresholds of toxicological concern for endocrine active substances in the aquatic environment

The threshold of toxicological concern (TTC) concept proposes that an exposure threshold value can be derived for chemicals, below which no significant risk to human health or the environment is expected. This concept goes further than setting acceptable exposure levels for individual chemicals, because it attempts to set a de minimis value for chemicals, including those of unknown toxicity, by taking the chemicals structure or mode of action (MOA) into consideration. This study examines the use of the TTC concern concept for endocrine active substances (EAS) with an estrogenic MOA. A case study formed the basis for a workshop of regulatory, industry and academic scientists held to discuss the use of the TTC in aquatic environmental risk assessment. The feasibility and acceptability, general advantages and disadvantages, and the specific issues that need to be considered when applying the TTC concept for EAS in risk assessment were addressed. Issues surrounding the statistical approaches used to derive TTCs were also discussed. This study presents discussion points and consensus findings of the workshop.

Mathematische Modelle zur Effektabschätzung

ZusammenfassungDie Extrapolation von toxikologischen Daten aus Labortests auf Schwellenwerte für Ökosysteme stellt ein zentrales Problem bei der Effektabschätzung im Rahmen der ökologischen Risikoanalyse dar. Die üblichen statistischen Verfahren werden kurz vorgestellt, bevor Beispiele zur Anwendung von Simulationsmodellen gegeben werden. Ein Verfahren zur Abschätzung von Schwellenkonzentration für verschiedene Endpunkte mit Hilfe von Monte-Carlo-Simulationen wird vorgestellt und an einem Datensatz für acht Chemikalien mit statistischen Verfahren verglichen. Abschließend werden die Vor-und Nachteile gegenübergestellt.AbstractThe extrapolation from single-species toxicity data to ecosystem thresholds is one of the principal problems in ecological risk assessment. The common statistical methods are briefly presented prior to a brief trial application of simulation models. A method for calculating ecosystem thresholds for different end points using Monte-Carlo simulations is applied to a data set of eight substances and subsequently compared with statistical approaches. Finally, a comparison of the pros and cons of such simulation models for extrapolation is presented.

Large-scale monitoring of effects of clothianidin-dressed oilseed rape seeds on pollinating insects in Northern Germany: justification of study design and statistical analysis

The commentary by Bailey and Greenwood makes several strong criticisms of the monitoring study of Heimbach et al. (2016), which are not applicable or misleading. These misrepresentations include the claim that the experimental design of this study was inappropriate and that the statistical analysis in the way it was conducted was senseless. Methods have been described in detail by Heimbach et al. (2016); Peters et al. (2016); Rolke et al. (2016a; b); Sterk et al. (2016) and the aspect of “pseudoreplication” has been discussed in Heimbach et al. (2016) and in detail in Rolke et al. (2016a). Therefore the criticism of Bailey and Greenwood does not add new facts to the scientific audience, overall. With this letter, we respond to the points of criticism discussing basic aspects of the study.